Global Decline of Big, Old Trees Impacts Forest Ecosystems

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Trees can live hundreds, even thousands of years. But the problem is that these trees aren’t making it to old age and according to a new study, big, old trees are in decline throughout the world which can have detrimental impacts to forest ecosystems.

Old trees are crucial organisms for many ecosystems: they provide homes for animals, provide space for other plants to grow, and they produce seeds, leaves, and nuts that serve as food. They also store large amounts of carbon and continue to sequester it as they grow, said study co-author David Lindenmayer, a researcher at Australian National University. One study published in PLoS ONE in May found that although big trees (with a diameter of more than 3 feet at chest height) made up only 1 percent of trees in a study plot in California's Yosemite National Park, they accounted for 50 percent of the area's biomass.
Another study found that huge mountain ash trees in southern Australia and Tasmania provide homes for more than 40 species of animals, Lindenmayer said.
"Large old trees are declining rapidly in all kinds of ecosystems worldwide — forests, rainforests, boreal forests, woodlands, agricultural areas, cities and savannahs," Lindenmayer told OurAmazingPlanet.
While forest fires or clear-cutting are often blamed for the loss of these trees, their disappearance is usually less apparent, said Nate Stephenson, an ecologist with the Western Ecological Research Center in Three Rivers, California. "Losses of big, old trees can take place over decades, generally too slowly for people to notice," said Stephenson. "The next generation may not know that big old trees were once common in the nearby forest."
Different regions around the world have different tree problems Lindenmayer said. "It might be elephants plus fire plus fungi in [South Africa's] Kruger National Park, versus fire plus logging plus climate change in the wet forests of Victoria," in Australia, he said.
From logging to clearing land for development or agriculture, to non-native insects or pathogens, trees are constantly being faced with potential threats. "But the problem manifests in broadly the same way in all systems: rapid loss of existing large old trees and often a failure to recruit new big trees, leading to a massive vacuum."
To prevent the loss of more forest giants, people need to protect these individuals and the places where they are more likely to grow, Lindenmayer said. It's also important that land managers realize the importance of big old trees. "Many managers have no idea about this," he said.
The study can be found in the journal Science.